The present invention relates generally to automotive HVAC systems for controlling the environment of an automobile passenger compartment. More particularly, the invention relates to an anti-fog control system for preventing the fogging of windows in a reversible HVAC system for automobiles.
This application is related to co-pending applications all filed on Nov. 12, 1998 and titled Refrigerant Flow Management Center For Automobiles, Reversible Air Conditioning And Heat Pump HVAC System For Electric Vehicles, Controller For Reversible Air Conditioning And Heat Pump HVAC System For Electric Vehicles, Controller For Heating In Reversible Air Conditioning And Heat Pump HVAC System For Electric Vehicles, Air Handling Controller For Hvac System For Electric Vehicles, and System For Cooling Electric Vehicle Batteries. Each of these applications is incorporated by reference into the present application.
Automotive climate control systems have traditionally been single loop designs in which the full volume of refrigerant flows through each component in the system. In operation refrigerant in the vapor phase is pressurized by a compressor or pump. The pressurized refrigerant flows through a condenser which is typically configured as a long serpentine coil. As refrigerant flows through the condenser, heat energy stored in the refrigerant is radiated to the external environment resulting in the refrigerant transitioning to a liquid phase. The liquefied refrigerant flows from the condenser to an expansion valve located prior to an evaporator. As the liquid flows through the expansion valve it is converted from a high pressure, high temperature liquid to a low pressure, low temperature spray allowing it to absorb heat. The refrigerant flows through the evaporator absorbing heat from the air that is blown through the evaporator fins. When a sufficient amount of heat is absorbed the refrigerant transitions to the vapor phase. Any further heat that is absorbed raises the vaporized refrigerant into the superheated temperature range where the temperature of the refrigerant increases beyond the saturation temperature. The superheated refrigerant flows from the outlet of the evaporator to the compressor where the cycle repeats. Generally, the refrigerant flowing into the compressor should be in the vapor phase to maximize pumping efficiency. Increasing the volume of refrigerant that flows through the valve lengthens the distance traversed by the liquid before it changes to the vapor phase, allowing the heat exchanger to operate at maximum efficiency.
Advances in automotive HVAC systems have led to zone temperature control systems in which different zones of an automobile are independently controlled. Zone control systems generally include an evaporator and expansion valve for each zone. The refrigerant flows through a compressor and condenser, then is split by a system of valves before flowing to the expansion valve and evaporator of each zone. The refrigerant flowing out of the evaporator of each zone is then recombined before returning to the compressor. A complex series of valves and plumbing is generally required to maintain a balanced HVAC system that provides individualized control for each of the zones.
With the advent of electric vehicles reversible heat pump systems have been introduced into automobiles. In a reversible heat pump system the HVAC system can either heat or cool a compartment depending on the direction of the refrigerant flow. In the air conditioning mode refrigerant flows from the compressor through an outside coil (condenser) and into an expansion valve and inside coil (evaporator) before returning to the compressor. Heat energy is extracted from air that is blown through the inside coil (evaporator) into the passenger compartment thus providing cooled air. In the heating mode a four way valve reverses the flow of refrigerant through the coils, thereby reversing the function of the coils. Refrigerant flows from the compressor through the inside coil (condenser) then into an expansion valve and the outside coil (evaporator) before returning to the compressor. Heat energy in the liquefied refrigerant flowing through the inside coil is absorbed by air that is blown through the coil into the passenger compartment thus providing heated air.
An inherent problem with reversible HVAC systems is the potential for fogging of the passenger compartment windows when the system switches from air conditioning mode into heat pump mode. During air conditioning mode the refrigerant flowing through the inside coil (evaporator) is much cooler than the warm air being blown through the coil. Therefore, moisture within the blown air condenses out of the air as it cools while passing through the coil. Some of the condensed moisture accumulates on the surfaces of the coil while the remainder drips to the ground. When the HVAC switches to heat pump mode the refrigerant which is routed through the inside coil, now functioning as a condenser, is significantly hotter than the air that is blown through the coil. The moisture that had accumulated on the inside coil is rapidly boiled off and absorbed by the air being blown through the coil. The moisture laden air is then blown into the passenger compartment where it almost instantaneously turns the vehicle windows into an opaque barrier.
One object of the present invention is to provide a system which controls fogging when changing modes in a reversible HVAC system.
Another object of the present invention is to disclose an anti-fogging method in which the rate of initial heating of the passenger compartment is not compromised.
It is an additional object of the present invention to provide a system which controls fogging in an HVAC system when initially starting air conditioning mode.
Accordingly, the invention solves the aforementioned problem by providing a method of controlling fogging in vehicles having a reversible HVAC system. First, the method detects if conditions for fogging exist such as moisture or localized coldspots on the inside heat exchanger. Then, the speed of the compressor is gradually increased, causing the discharge temperature of the refrigerant to increase at a controlled rate. As the temperature of the refrigerant increases, the temperature of the inside heat exchanger increases. Moisture that exists on the inside heat exchanger slowly begins to evaporate into the air passing through the heat exchanger into the passenger compartment. The moisture laden air flows through the passenger compartment and exits through door seal cracks and outlet vents to the outside environment. After a predetermined period of time, the moisture on the inside heat exchanger has evaporated, so the compressor speed is increased to its steady-state speed.
The above described method is only an example. Methods in accordance with the present invention may be implemented in a variety of ways.